Alkyl carbamates are widely used to prepare chemical intermediates. For example, methyl carbamate can be used for the synthesis of melamine derivatives, polyethylene amine, furthermore, methyl carbamate can also be reacted with unsaturated hydrocarbons, aldehydes, ketones, multifunctional alcohols and aryl rings to afford various derivatives. Ethyl carbamate can be used to synthesize alkanediol dicarbamates, a promising class of tranquilizing drugs (Sidney Beinfest et al, preparation of organic mono-carbamates, U.S. Pat. No. 2,837,561). Butyl carbamate may be reacted with formaldehyde to form methylol derivates that are effective as textile crease-proofing agents (Max Robeson etc. production of alkyl carbamate, U.S. Pat. No. 3,574,711). In addition, the alkyl carbamates can be used for the synthesis of the corresponding organic carbonates, or be used as new kind of carbonyl sources for the synthesis of isocyanates.
Due to the alkyl carbamates' wide application, the methods for preparing the alkyl carbamates received much concern in the industry. U.S. Pat. No. 4,242,520 disclosed a method for preparing the alkyl carbamates by reacting amine with carbon monoxide and alcohol in the presence of catalyst, however, this method might potentially harm the producers and users' health, due to the fact that the carbon monoxide his a toxic gas.
Alcoholysis of urea is another mature method to produce alkyl carbamates, which produces alkyl carbamates by reacting urea with hydroxyl group containing compounds under suitable reaction conditions, and avoids using carbon monoxide in the preparation. This method can be used in the presence of catalyst, including ZnO disclosed in U.S. Pat. No. 3,574,711, Cu(OAc)2 disclosed in U.S. Pat. No. 2,837,561 and U.S. Pat. No. 3,013,064, a complex of transition metals oxides and acids disclosed in U.S. Pat. No. 3,554,730, the catalyst system of nano-TiO2 and R3N disclosed in CN1365969, and oxides such as MgO, CaO, ZnO, PbO disclosed in CN1475481.
However, the catalysts used in alcoholysis of urea are not so good, due to the fact that the problems of relative low yields of desired products, catalyst separation and catalyst recycling use were not solved well. Therefore, from view of industry practice, it is more and more desirable to develop a kind of catalysts for the synthesis of alkyl carbamates, wherein the catalysts are not only highly effective but also can be easily recovered from the reaction mixture and reused.